Accession No
3270
Brief Description
dividing engine, in style of Ramsden’s second engine, English, c. 1800
Origin
England; [London]
Maker
after Ramsden
Class
metrology; navigation
Earliest Date
1793
Latest Date
1819
Inscription Date
Material
wood (2 types); metal (cast iron, brass, bronze (?), at least one other)
Dimensions
height 1181mm; breadth 859mm; depth 935mm
Special Collection
Provenance
Donated by 'Henry Hughes and Sons', [a division of:] Kelvin & Hughes, Chigwell, Essex, England, 1954(?). The engine was acquired by the firm of Henry Hughes and Son at some point in the nineteenth century and was in operation until c. 1945 [letter from Derek Price to Whipple Museum in 1968 says it was “in use right through World War II dividing sextants”].
Inscription
Description Notes
Dividing engine, in style of Ramsden’s second engine, English, c. 1800.
Triangular wooden table supports triangular cast-iron frame. Set on the frame is a circular wooden board, with a guard running around its edge, within which the wheel of the engine is positioned. One apex of the frame carries two cast-iron downward extensions, joined at their lower ends by a plate; these extensions supports the pivot for the cast pillar which carries the endless screw and ratchet mechanism.
Horizontal bronze (?) wheel with 12 spokes, the weight of the wheel being carried by three brass wheels which bear on the bottom of the inner circle of the frame. The wheel has a separate brass rim with 2160 teeth; also a degree scale divided [0] - [360˚], numbered by 10˚, subdivided to 30´.
Set on the top of the cast iron extensions is the endless screw with a central threaded section. This carries at one end a dial which is divided into 10 major divisions of 12 subdivisions (the latter equivalent to a 5-second rotation of the wheel). At the other end of the screw is a ratchet mechanism. Set across the screw and passing into the centre of the wheel are two white metal rods which are held apart by a white metal rod at their inner ends (their length across the circle can be adjusted by knurled brass screws at their outer ends). These rods form the cutter frame.
Two brackets at opposite sides of the outside of the wooden guard carry two short cast-iron pillars which in turn support a diametrical iron support bar, which would have supported the cutter frame by means of a thin metal strip. (These bars are not currently in position.)
Condition poor/fair; incomplete.
References
Joshua Nall; ‘Astronomy at Sea’; Explore Whipple Collections online article; Whipple Museum of the History of Science; University of Cambridge; 2020: https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/astronomy-and-empire/astronomy-sea
Events
Description
This instrument is one of the earliest mechanical dividing engines still surviving. In the 18th century demand for scientific instruments with precisely divided scales greatly increased. Instrument manufacturers struggled to keep pace, especially in the supply of the definitive new navigational tool, the sextant, which carried a scale so finely divided it could aid in the determination of longitude by the ‘lunar method'. Famed London instrument maker Jesse Ramsden pursued a revolutionary solution to this bottleneck - instead of laboriously dividing each instrument’s scale by hand (a process that took weeks), Ramsden designed and built a machine that could match the maker’s precision—in a matter of hours. Much of Ramsden's work building the ‘dividing engine’ was funded by the Board of Longitude. Once the machine had proven effective the Board insisted that copies of Ramsden’s engine be made and used by other London makers, so that many more sextants and similar instruments could be manufactured quickly and economically for Britain’s growing navy and merchant fleet. This instrument is believed to be one of these original copies, utilising Ramsden’s design of 2160 precisely spaced teeth around the edge of a revolving wheel engaged by an endless screw, capable of turning at precise fractions of a degree and then marking an instrument fixed to it.
Wh.3270 was a gift to the museum in the mid 1950s from Mr Arthur J. Hughes, President of Henry Hughes & Sons Ltd, makers of navigating instruments in London. This particular machine, built some time around 1800, was in use through World War II dividing sextants.
06/06/2017
Created by: Josh Nall on 06/06/2017
FM:44953
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